It is known that olefins, including ethylene, can be polymerized with catalyst compositions employing titanium, zirconium, vanadium, chromium or other metals, impregnated on a variety of support materials, often in the presence of cocatalysts. These catalyst compositions may be useful for both homopolymerization of ethylene, as well as copolymerization of ethylene with comonomers such as propylene, 1-butene, 1-hexene, or other higher α-olefins. Therefore, there exists a constant search to develop new olefin polymerization catalysts, catalyst activation processes, and methods of making and using catalysts, that will provide enhanced catalytic activities and polymeric materials tailored to specific end uses.
One type of catalyst system comprises organometal compounds, particularly metallocene compounds. A special class of metallocenes that has been little explored are the half-sandwich metallocenes, which contain only a single η5-cyclopentadienyl-type ring system. It is believed that such compounds may offer the potential for higher activity and better comonomer incorporation. Also of interest is the development of metallocene-based catalytic systems that can be activated with a variety of activating agents without requiring relatively expensive methylaluminoxane, yet still provide relatively high polymerization activities.
Therefore, what are needed are new catalyst compositions and methods of making the catalyst compositions that afford high polymerization activities, and will allow polymer properties to be maintained within the desired specification ranges.